1. Field of the Invention
This invention relates to catalyst systems including ruthenium salts and aluminum halides; the aluminum halides include both nonalkylated and alkyl aluminum halides. These catalyst systems are employed in the codimerization of alpha-monoolefins and conjugated diolefins to yield 1,4-dienes.
2. Description of Material Information
Nonconjugated diolefins, including the 1,4-dienes, can be employed for a variety of purposes. The trans-isomers of 1,4-dienes are useful as polymerization starting materials; cis-1,4-dienes, however, impact unfavorably on the desired reaction.
As a particular example, trans-1,4-hexadiene is useful in the production of functionalizable polymers, and is employed in preparing EPDM terpolymer. Cis-1,4-hexadine, however, has a deleterious effect on polymerization catalysts, and, moreover, is difficult to separate from trans-isomer.
1,4-dienes can be obtained from codimerization of alpha-monoolefins and conjugated dienes; specifically, 1,4-hexadiene is yielded from ethylene and 1,3-butadiene. Because of the desirability of the trans-isomers and the undesirability of cis-isomers, codimerizations selective for the former are preferred; the less cis-isomer produced relative to trans-isomer, the more desirable the reaction.
The requisite codimerization may be carried out by a variety of methods, including anionic, cationic, and transition metal-catalyzed processes. Of particular relevance are codimerizations conducted in the presence of soluble transition metal salts; a variety of such processes are known in the art.
Codimerization catalyst systems utilizing different Group VIII metals, including systems which are selective to the trans-isomer, are known. U.S. Pat. Nos. 3,640,898 and 3,742,080 both disclose a catalyst system yielding 1,4- dienes in high trans to cis ratio, comprising a rhodium (III) salt and at least one promoter selected from amides, phosphoramides, phosphine oxides, and water. However, the high cost of rhodium makes such catalyst systems undesirable.
Catalyst systems particularly utilizing ruthenium compounds are also known. U.S. Pat. No. 3,523,983 discloses a catalyst system comprising a ruthenium salt, dissolved in a hydrocarbon solvent, incorporating a proportion of water, hydrogen, or hydride, such as alkali metal aluminum hydride. U.S. Pat. No. 3,361,840 discloses a salt of a Group VIII metal, such as ruthenium, and an organic nitro compound in substantially anhydrous liquid medium. Canadian Patent No. 691,770 discloses solutions of Group VIII noble metal salts, including various specified ruthenium salts, as dimerization catalyst systems. However, none of these references discloses or suggests either the presence of an alkyl aluminum halide in conjunction with the ruthenium salt component of the catalyst system, or the use of the catalyst system for the synthesis of 1,4-dienes.
It has been discovered that catalyst systems incorporating both ruthenium salts and aluminum halides, including the alkyl aluminum halides as well as the nonalkylated aluminum halides, are characterized by both high activity and high trans-selectivity in the codimerization of alpha-monoolefins and conjugated dienes. Particularly as to the codimerization of ethylene and 1,3-butadiene, selectivities as high as 20:1 trans to cis, and higher, may be achieved.